Interpretation #7677
Published November 06, 2015
Original Request
- Code Version
- 2010
- Code
- BUILDING
- Code Description
- Building
- Chapter
- 7
- Section
- 708.2
- Topic
- Rating of ducts with dampers
Question
Is it the intent of 708.2 to require that all horizontal ducts leaving a 2-hour shaft be enclosed in rated construction if the where the duct leaves the shaft, it is protected by a UL listed rated fire & smoke damper?
Answer Published 11/06/2015 at 1:07 PM
Yes, it is the intent of the Code to enclose the duct until
is gets to its exit point at the roof. Adding a fire damper
at the underside of the roof is not acceptable.
The Mechanical Code, Section 607.5.5 states, "Shaft
enclosures that are permitted to be penetrated by ducts and
air transfer openings shall be protected with approved fire
and smoke dampers." The key word is "permitted."
is gets to its exit point at the roof. Adding a fire damper
at the underside of the roof is not acceptable.
The Mechanical Code, Section 607.5.5 states, "Shaft
enclosures that are permitted to be penetrated by ducts and
air transfer openings shall be protected with approved fire
and smoke dampers." The key word is "permitted."
Commentary
Refer to section 607.5.5 2014 FBC (M), also, look at 607.5.2
Fire barriers. In the Building volume, 713.7.1: "Openings
other than those necessary for the purpose of the shaft
shall not be permitted in shaft enclosures." At the top of
a riser, per the requester, "At the 11th floor ceiling, the
ducts exit the shafts and offset horizontally to the roof
top unit above." The offset may be necessary, but leaving
the shaft is not necessary. Entry points such as individual
exhaust ducts connected to the riser do need to penetrate
the shaft for obvious reasons. An offset at the top does
not need to penetrate the shaft if the shaft offsets along
with the duct. Therefore the penetration of the shaft at
the top, as described is not allowed with or without a fire
damper.
Further, the source Code for all this magnificence is NFPA
90A. In NFPA 90A, 5.3.4.1 states, "air ducts that pass
through the floors of buildings that require the protection
of vertical openings shall be enclosed with partitions..."
The main duct - whether it offsets or not at the top - does
pass through floors that require the protection of vertical
openings. It must therefore be enclosed all the way to the
roof deck to include the horizontal offset.